Watertight disc coaxial cable

ABSTRACT

A coaxial cable consists of a plurality of discs of a dielectric synthetic resin material that bonds to metal bonded to an elongated metal center conductor respectively at spaced intervals therealong. A tubular metal outer conductor encloses the discs and is bonded thereto so that the discs define a plurality of separate watertight compartments. An inner tubular sheath of a synthetic resin may be between, and bonded respectively to, the inside of the outer conductor and the discs. Also, a layer of synthetic resin may be bonded around the exterior of the outer tubular conductor.

United States Patent J achimowicz et a1.

WATERTIGHT DISC COAXIAL CABLE Inventors:

Olszewski, Bayonne, both of NJ.

General Cable Corporation, New York, N.Y.

Filed: Sept. 29, 1969 Appl. No.: 861,792

Assignee:

U.S. Cl ..174/28, 174/107, 333/96 Int. Cl. ..l-lOlb 11/18 Field of Search ..174/23, 28, 29, 102, 107, 120, 174/1015; 156/54, 51; 333/84, 96, 99;

References Cited UNITED STATES PATENTS 6/1958 Busse et a1. 154/139 5/1964 Graham et al..

l/l969 Peacock 1/1968 Volk ..l74/29 DISC APPLYING APPARATUS Ludwik Jachimowicz, Elizabeth; Jerzy A.

[451 May 2, 1972 FOREIGN PATENTS OR APPLICATIONS 733,178 7/1955 Great Britain ..174/29 879,712 10/1961 Great Britain.... ...174/28 990,002 4/ 1965 Great Britain 1 74/28 Primary Examiner-Lewis H. Myers Assistant Examiner-A. T. Grimley Attorney-Sandoe, Hopgood & Calimafde [5 7] ABSTRACT A coaxial cable consists of a plurality of discs of a dielectric synthetic resin material that bonds to metal bonded to an elongated metal center conductor respectively at spaced intervals therealong. A tubular metal outer conductor encloses the discs and is bonded thereto so that the discs define a plurality of separate watertight compartments. An inner tubular sheath of a synthetic resin may be between, and bonded respectively to, the inside of the outer conductor and the discs. Also, a

layer of synthetic resin may be bonded around the exterior of the outer tubular conductor.

7 Claims, 6 Drawing Figures Patented May 2, 1972 I nn DISC APPLYING APPARAT WATERTIGHT DISC COAXIAL CABLE BACKGROUND OF THE INVENTION The present invention is a coaxial cable which is watertight so as to be suitable for outdoor use and which has a low attenuation for high-frequency currents.

It is possible to provide a moisture-tight coaxial cable wherein the center conductor is surrounded by foamed polyethylene insulation to form a core which is enclosed in an aluminum tube that serves as the outer conductor of the coaxial pair. The attenuation of this cable, however, is high due to the use of solid or semi-solid insulation, such as foamed polyethylene which has a dielectric constant of about 1.5.

Attenuation is reduced substantially if air is used as the dielectric, and at least two types of coaxial cables are known in which an air dielectric is provided by having the outer tubularconductor around spacing discs of dielectric material which are placed on the center conductor at regular intervals (about 1 inch apart, for example) along it.

PRIOR ART The discs in these known types have customarily been made of polyethylene, which is relatively inexpensive and easily moldable. In one known construction the outer tubular conductor is made of an elongated strip of copper having its edge portions bent up around the discs to form a tube over which one or two steel tapes are helically wound. In another similar type the outer conductor is formed of a corrugated laminate of steel and copper strips. The edge portions of the laminate are bent around the disc to form a tube, the adjacent edges being soldered together in a seam. These forms of air dielectric cables however are unsuitable for use outdoors or in other places where they would be subject to moist conditions, because moisture, which may enter through a cable connector or through a tear or break in the outer conductor, for example, can migrate around the discs and along through the interior of the cable.

BRIEF SUMMARY OF THE INVENTION A principal object of the present invention is to p ovide a coaxial cable having an air dielectric and which thus has low attenuation and in which any moisture which may get into the cable cannot migrate along it, so that the cable is adapted for use outdoors and in moist conditions.

A coaxial cable in accordance with this invention consists of a lurality of discs of a dielectric material, which is moldable and which bonds to metal, spaced along the center conductor and bonded to the center conductor and to the tubular outer conductor. The discs thus form watertight compartments along the length of the cable.

DESCRIPTION OF THE DRAWINGS The coaxial cable of this invention and a method of making it will now be described in detail with reference to the accompanying drawings in which:

FIG. 1 is a schematic drawing showing the several steps of a method of forming the coaxial cable in accordance with the DETAILED DESCRIPTION OF THE INVENTION As best seen in FIGS. 3 and 4, a coaxial cable in accordance with this invention comprises generally a center conductor wire 11 having spacer discs 12 of dielectric material on it at spaced intervals (of about 1 inch, for example), and a tubular outer conductor 13 around the circumferences of the discs 12.

The center conductor wire 11 is suitably copper, copperclad aluminum or aluminum. The tubular outer conductor 13 is suitably aluminum or a steel and copper laminate. The spacer discs 12 are a moldable dielectric material which can be bonded permanently to metals, particularly to aluminum and copper, and to synthetic plastics, by theapplication of heat and pressure. Suitable materials for discs 12 are ionomers, such as the ionomer available from E. I. du Pont de Nemours and Co. under the trademark Surlyn, and copolymers of ethylene and a monomer containing acrylic acid, such as the copolymer identified by the designation QX-2375 available from Dow Chemical Company.

In accordance with the invention, the discs 12 are bonded both to the center conductor 11 and to the tubular outer conductor 13, so that the air dielectric of the cable is provided by a plurality of separate watertight compartments 14 along the length of the cable. Thus, water or moisture getting into the cable at any point through a connector or through a break or tear through the outer conductor 13, for example will be confined to the compartment 14 it enters. By thus limiting the length of the portion of the cable affected by any water or moisture getting into it, the reliability of the cable is greatly increased. For example, entry of moisture into the cable assuming the amount is not enough to cause a short circuit produces an impedance discontinuity which affects transmission in proportion to the physical lengthof the discontinuity expressed in terms of wavelength. At 300 MC the wavelength is about 1 meter. With the spacer discs 12 one inch apart, if moisture gets into one of the compartments 14, the length of the cable afiected by the moisture is 2.5 cm/lOO of the wavelength, which is not enough to produce significant deterioration of transmission. A discontinuity of one-fourth wavelength would have a more significant effect, but to produce a discontinuity, of this magnitude ten of the l-inch compartments 14 would each have to be punctured.

In accordance with the method of forming a coaxial cable 10 of this invention, the spacing discs 12 are pressure-molded onto the center conductor 11, while the center conductor 11 is heated sufficiently for the heat and pressure of the molding to bond the discs to the conductor. The conductor may be preheated if necessary, but the heat of the pressure-molding operation will normally heat the center conductor to the extent required.

The center conductor 11 with the discs 12 thereon is then enclosed by the tubular conductor 13. This may be done either by drawing the center conductor and discs into a preformed tubular outer conductor 13 or by bending the edge portions of an elongated strip of outer conductor material around the circumferences of the discs and welding or soldering the adjacent edges of the strip together. In either case, as initially formed or provided, the inside diameter of the outer conductor 13 is larger than the outside diameters of the discs, so that there is a space 15 between, as illustrated in FIG. 2. Thereafter, the diameter of the outer tubular conductor 13 is reduced by die-sinking, or by any other suitable method, to shrink it down into intimate pressure contact with the circumferences of the discs 12. The outer conductor 13 is then heated to complete the bond between the discs 12 and the inside of the tubular outer conductor 13.

FIG. 1 illustrates schematically apparatus for making the above-described coaxial cable in accordance with a method of this invention. The discs 12 are pressure-molded onto the center conductor 11 by disc-applying apparatus indicated at 16 The conductor 1 l, with discs 12 thereon, and a continuous strip 17 of aluminum, or other suitable metal, for the outer tubular conductor 13 are brought together and fed through a pair of forming rolls 18, which start the bending of the edge portions of the strip 17 up around the circumferences of the discs 12. From the rolls 18, the partially formed cable is drawn through tube-forming dies 19, which bring the opposite edges of the strip 17 together to be welded into a seam at a successive welding station 20. At this point the tubular outer conductor 13 is a larger diameter than the disc 12, as indicated in FIG. 2, and is then die-sunk down into intimate pressure contact with the discs 12, as illustrated in FIG. 3, by being drawn through sinking dies 21. Movement of the cable 10 through the rolls 18, dies 19, welding station 20 and dies 21 is provided by conventional forwarding means, such as a caterpillar forwarding device 22 engaging the tubular outer conductor 13 of the cable.

After the outer conductor 13 is sunk into pressure contact with the discs 12, it is heated at a heating station 23, for example, to complete the bond between the circumferences of the discs 12 and the outer conductor 13. In a preferred form of the cable, however, the exterior of the tubular outer conductor 13 is provided with an outer protective jacket 24 of polyethylene, illustrated in FIG. 4, and it has been found that the heat provided by extruding the polyethylene jacket onto the tubular outer conductor 13 is enough to cause satisfactory bonding of the discs 12 to the tubular outer conductor 13.

FIG. illustrates another embodiment of a cable of this invention wherein, after the discs 12 are pressure-molded onto the center conductor 11 and prior to putting on the tubular outer conductor 13, a thin-walled tube 25 of material, which is the same as or similar to the material of the discs 12, namely, moldable material which will bond to metal and synthetic plastics under heat and pressure, is extruded over the circumferences of the discs 12 so as to become bonded thereto. The wall of this tube 25 is suitably to mils thick, for example.

The tubular outer conductor 13 is then applied over the tube 25, die-sunk into intimate pressure contact therewith, and bonded to it by applying heat, as described above. The inner tube being thus bonded to both the circumferences of the discs 12 and to the inside of the tubular outer conductors 13 bonds the tubular outer conductor to the discs. The inclusion of this tube 25, of course, increases the expense due to the extra material and the additional extruding step. It also increases slightly the attenuation due to the presence of the additional quantity of dielectric in the space between the outer conductor 13 and the center conductor 11. But the addition of this tube 25 provides a higher degree of protection against moisture and thus increases the reliability of the cable.

As mentioned above, an outer protective jacket of polyethylene, illustrated by the jacket 24 in FIG. 4, may be applied over the tubular outer conductor 13 for adding reinforcement. FIG. 6 illustrates another modification in which an outer protective jacket 24a of polyethylene is bonded to the tubular outer conductor 13 by means of an intermediate layer 26 of the aforementioned type of moldable material which will bond to metal and plastic under heat and pressure. In this embodiment the layer 26 of the moldable material is extruded over the tubular outer conductor 13, the heat of the extrusion process normally being sufficient for the layer 26 to bond to the tubular outer conductor 13. Then the outer jacket 24a of polyethylene is extruded over the layer 26,.the heat of the extrusion process also normally being sufiicient to bond the layer 26 to the jacket 24a.

This invention provides a coaxial cable in which the dielectric between the center conductor 11 and the tubular outer conductor 13 is approximately ninety per cent air with the discs 12 spaced about 1 inch apart along the center conductor 11, which thus provides a cable which has low attenuation for high frequency currents (on the order of from about 3 to 300 MHz, for example). Moreover, this cable is particularly adapted for use outdoors or in moist conditions, since the numerous small watertight compartments 14 along the length of the cable severely limit the possibility of water or moisture getting in. But, if water or moisture should get in, it is confined to a small section and is prevented by the sealed discs 12 from migrating along inside the cable.

What is claimed is:

1. A coaxial cable comprising an elongated center conductor having a plural it of flat imperforate discs of dielectric material camed axi ly thereon respectively at spaced intervals therealong and bonded to the center conductor, and a tubular outer conductor that contacts with the circumferences of the discs to compress the discs toward the center conductor, said discs each being bonded around its circumference to said outer conductor to form a plurality of separate watertight compartments along the cable.

2. The cable of claim 1 in which: at least the exterior of the center conductor is copper, the outer conductor is aluminum, and the discs are a synthetic resin material molded on the center conductor and having their axial spacing from one another of the order of one-fourtieth of the wave length with which the cable is intended to be used.

3. The cable of claim 2 in which the synthetic resin material is from the group consisting of ionomer resins and of copolymers of ethylene and monomers containing acrylic acid.

4. The cable of claim 1 including an inner tubular sheath of synthetic resin material between and bonded respectively to the inside of the outer conductor and the discs.

5. The cable of claim 1 includingan outer tubular sheath of synthetic resin material over the outside of the outer conductor and bonded thereto.

6. The cable of claim 5 in which said outer tubular sheath comprises an inner layer of a resin material from the group consisting of ionomer resins and of copolymers of ethylene and a monomer containing acrylic acid and an outer layer of polyethylene, said inner layer being bonded to both the outer conductor and to said outer layer of polyethylene.

7. The cable of claim 5 in which said outer tubular sheath is a resin material from the group consisting of ionomer resins and of copolymers of ethylene and a monomer containing I acrylic acid.

' UNITED STATES PATENT. OFFICE CERTIFICATE OF CORRECTION Patent 3,6603589 o Dated May 2, 1972 Inventor(s) Ludwik Jachimowicz. et 31 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

C v Signed and sealed this 21st day of November 1972.

Column 2, line 34 after the sign, should read (SEAL) Attesc:

EDWARD M.FLETCHER,-JR. e ROBERT GOITSCHALK Attesting Officer Commissioner of Patents FORM PO-1050 (10-69) USCOMM-DC wan-p es a U.S. GOVERNMENT PRINTING OFFICE: I969 0 3G6-334,

UNITED STATES ATENT oFFicE QERTEHCAT O ETEN Patent No. 3, ,5 9 Dated May 2, 1972 Ludwik Jachimowicz et 211 Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 34 after vthe sign, should read l uo Signed and sealed this 21st day of November 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GO'I'TSCHALK Attesting Officer I Commissioner of Patents FORM PO'WSO USCOMM-DC eosnmpeo U. GOVERNMENT PRINTING OFFICE: I969 0-366-334, 

1. A coaxial cable comprising an elongated center conductor having a plurality of flat imperforate discs of dielectric material carried axially thereon respectively at spaced intervals therealong and bonded to the center conductor, and a tubular outer conductor that contacts with the circumferences of the discs to compress the discs toward the center conductor, said discs each being bonded around its circumference to said outer conductor to form a plurality of separate watertight compartments along the cable.
 2. The cable of claim 1 in which: at least the exterior of the center conductor is copper, the outer conductor is aluminum, and the discs are a synthetic resin material molded on the center conductor and having their axial spacing from one another of the order of one-fourtieth of the wave length with which the cable is intended to be used.
 3. The cable of claim 2 in which the synthetic resin material is from the group consisting of ionomer resins and of copolymers of ethylene and monomers containing acrylic acid.
 4. The cable of claim 1 including an inner tubular sheath of synthetic resin material between and bonded respectively to the inside of the outer conductor and the discs.
 5. The cable of claim 1 including an outer tubular sheath of synthetic resin material over the outside of the outer conductor and bonded thereto.
 6. The cable of claim 5 in which said outer tubular sheath comprises an inner layer of a resin material from the group consisting of ionomer resins and of copolymers of ethylene and a monomer containing acrylic acid and an outer layer of polyethylene, said inner layer being bonded to both the outer conductor and to said outer layer of polyethylene.
 7. The cable of claim 5 in which said outer tubular sheath is a resin material from the group consisting of ionomer resins and of copolymers of ethylene and a monomer containing acrylic acid. 